Its electrons say we won't find anything beyond the Standard Model at the LHC.

Are there any particles beyond the Higgs lurking where the LHC might discover them? A team of researchers that calls itself the ACME project has now produced a measurement that says the answer is "probably not." ACME looked for any imperfections in the shape of an electron's electric field and placed a limit on the measurements that is 12 times smaller than anyone had previously achieved. As far as they could tell, the electron has no imperfections, which rules out the possibility of finding many of the new particles predicted to be within the mass range that will be explored by the LHC.

The research relied on thorium atoms, which are mostly discussed as a potential nuclear fuel. But in this case, the authors were after the electrons. Thorium's high atomic number means that its innermost electrons orbit within an intense electric field that's internal to the atom, and they travel at relativistic speeds. These properties will serve to exaggerate even a minuscule imperfection in the electric field of the electron itself.

The imperfection the ACME team was after is called the electric dipole moment, and it's measured relative to the electron's spin. If the electron has an electric dipole moment, then its charge will be unevenly distributed along its spin. Nothing in the Standard Model can create an electron dipole moment, but most extensions to the Model, including Super Symmetry, posit heavier particles, the mere existence of which should alter the dipole moment.

To measure it, the ACME team built a device that could send a beam of cold thorium oxide molecules into a device. As the atoms entered, they were zapped with lasers that could create a specific transition in one of the thorium's inner electrons, affecting its spin. The atoms then passed between some plates that created an electric field. If the electron has an electric dipole moment, the resulting imperfection will interact with this electric field, changing how the orientation of the spin changes with time. The spin is read out with a second laser at the far end of the device, allowing the researchers to search for any signs of unexpected changes.

After building up a huge number of measurements, the authors searched through them for potential sources of error, identifying a few and correcting for them. They also added a constant value to their calculations that should throw them off, but the team kept themselves blind to it—this kept their own expectations from influencing how they conducted the experiment.

When all was said and done, no sign of an electric dipole moment was apparent. That means that, if one exists, it must be smaller than the experimental error of these experiments. And that experimental error is 12 times smaller than the one set by previous experiments.

That's a significant result, even though it was generated with equipment that just fills up a couple of bench tops. An electron dipole moment isn't predicted by the Standard Model, but it can arise from a new form of charge-parity violation. As the ACME team puts it, "Nearly every extension to the [Standard Model] introduces new CP violating phases." So, those extensions dictate that the electron should have an electric dipole moment. The smaller the dipole moment, the heavier the particle involved in its creation.

Thus, by lowering the size of the largest possible electric dipole moment, the new results rule out lighter forms of most of the particles people have predicted. In fact, they rule out finding them in the LHC entirely: "our more precise [electric dipole moment] limit constrains CP violation up to energy scales similar to or higher than those explored directly at the Large Hadron Collider." That doesn't mean we can't find any new particles there, but it does indicate that the search for the ones that are relatively easy to predict on theoretical grounds is likely to come up blank.

Because the sooner the brightest minds in the field quit looking for Wimps, and concentrate on looking for it somewhere else; then the sooner we will have some exciting new science.

Hopefully, within my lifetime.

It's not so simple as that, since Dark Matter is merely a descriptor for a phenomena we don't know about. WIMPs are merely one attempt at explaining the Dark Matter problem. Indirectly, via cosmic observations of large scale formations of galaxies and superclusters, we know there is Dark Matter. The universe just couldn't be in its current form without a huge pile of the stuff (and a lot more of it than normal matter).

Saying this is a blow for Dark Matter is wrong. It might be a blow for one of the possible explanations, but that's not to say other explanations will be affected. Also, never discount on Nature's ability to throw curveballs. Reality is truly stranger than fiction...

Because the sooner the brightest minds in the field quit looking for Wimps, and concentrate on looking for it somewhere else; then the sooner we will have some exciting new science.

Hopefully, within my lifetime.

It's not so simple as that, since Dark Matter is merely a descriptor for a phenomena we don't know about. WIMPs are merely one attempt at explaining the Dark Matter problem. Indirectly, via cosmic observations of large scale formations of galaxies and superclusters, we know there is Dark Matter. The universe just couldn't be in its current form without a huge pile of the stuff (and a lot more of it than normal matter).

Saying this is a blow for Dark Matter is wrong. It might be a blow for one of the possible explanations, but that's not to say other explanations will be affected. Also, never discount on Nature's ability to throw curveballs. Reality is truly stranger than fiction...

We don't 'know' there is dark matter despite these observations. Another explanation instead of dark matter is modified gravity of some sort over the large scale.

However as far as I know, there is a LOT less going for modified gravity explanations. And besides, I'd argue it still falls under the Dark Matter umbrella term, because it is just another attempt at explaining a specific set of "strange shit" (yes, very technical term there ).

We don't 'know' there is dark matter despite these observations. Another explanation instead of dark matter is modified gravity of some sort over the large scale.

Nope. That approach has already failed spectacularly. Every galaxy would need its own modified version of gravity, it doesn't explain microlensing observations at all, it produces wildly incorrect predictions for the distribution of matter, and it fails to explain some details of nucleosynthesis that dark matter explains.

We don't 'know' there is dark matter despite these observations. Another explanation instead of dark matter is modified gravity of some sort over the large scale.

Nope. That approach has already failed spectacularly. Every galaxy would need its own modified version of gravity, it doesn't explain microlensing observations at all, it produces wildly incorrect predictions for the distribution of matter, and it fails to explain some details of nucleosynthesis that dark matter explains.

Dark matter is real, it just probably isn't supersymmetric particles.

What about an immense number of non-relativistic neutrinos left over from the big bang?

We don't 'know' there is dark matter despite these observations. Another explanation instead of dark matter is modified gravity of some sort over the large scale.

Nope. That approach has already failed spectacularly. Every galaxy would need its own modified version of gravity, it doesn't explain microlensing observations at all, it produces wildly incorrect predictions for the distribution of matter, and it fails to explain some details of nucleosynthesis that dark matter explains.

Dark matter is real, it just probably isn't supersymmetric particles.

What about an immense number of non-relativistic neutrinos left over from the big bang?

More likely it's the immense stockpile of lumps of coal wating to be delivered all the bad little girls and boys each Christmas.

An Oraison is a meditative prayer in french, the Continuum is a micro-tonal XYZ controller, the synth use analog voltage "logic" and some opto-electronic: it's nearly impossible to get exactly the same result each time you perform.

This report also reminds me to check up on the lesser known sister detector at the LHC to ATLAS and CMS called LHCb. It tries to explore the issue of CP-violation in more detail, and it tries to find more decay channels that violate CP. If new physics were to be found at at the LHC, that detector is most likely to do that.

We don't 'know' there is dark matter despite these observations. Another explanation instead of dark matter is modified gravity of some sort over the large scale.

Nope. That approach has already failed spectacularly. Every galaxy would need its own modified version of gravity, it doesn't explain microlensing observations at all, it produces wildly incorrect predictions for the distribution of matter, and it fails to explain some details of nucleosynthesis that dark matter explains.

Dark matter is real, it just probably isn't supersymmetric particles.

What about an immense number of non-relativistic neutrinos left over from the big bang?

Doesn't work. Neutrinos would count as hot dark matter (since they're traveling at relativistic speeds), which doesn't explain many of the phenomenon we see with dark matter.

In addition, they don't have enough mass/energy to explain dark matter either. Their contribution to the energy density of the universe drops off according to the fourth power of expansion, just the same as photons do*, so by now they only have a tiny (order of magnitude 10^-5, IIRC) fraction of the total energy of the universe, unlike dark matter, which has around 26% of the energy density of the universe right now.

*This is because most of their energy is kinetic, and as the universe expands they slow down ("redshift", so to speak), so they lose energy individually, as well as falling in density from the expansion.

If there's one team I'll trust in with matters of physics it's one based on Wile E. Coyote. I mean let's face it, he may be immortal but still finds a way to have real world physics apply to him when gravity or walls are involved.

Though I do hope they didn't make their own products. The ACME name has seen better days.

We don't 'know' there is dark matter despite these observations. Another explanation instead of dark matter is modified gravity of some sort over the large scale.

Nope. That approach has already failed spectacularly. Every galaxy would need its own modified version of gravity, it doesn't explain microlensing observations at all, it produces wildly incorrect predictions for the distribution of matter, and it fails to explain some details of nucleosynthesis that dark matter explains.

Dark matter is real, it just probably isn't supersymmetric particles.

According to the STVG page, the current version of the modified-gravity theory seems to be holding up well. But I don't know much about it beyond that, so if you have any links to things it doesn't address, I'd appreciate it.

They found the Higgs boson at 126 GeV, and the LHC itself runs up to about 7 TeV, although it's hard to picture it having much resolution beyond about 1 TeV. (For comparison, Fermilab was rated at 1 TeV total, but could only find hints of the Higgs in the 120-140 GeV range and couldn't pin it down.) My guess is this puts the floor at not less an 700 GeV, which is huge, but it would be interesting to know the number because it could be much higher.

It takes a lot to get to macroscopic numbers, with 1J=6.2E18 eV, although that can be seen in exoenergy protons from space.

What about an immense number of non-relativistic neutrinos left over from the big bang?

Doesn't work. Neutrinos would count as hot dark matter (since they're traveling at relativistic speeds), which doesn't explain many of the phenomenon we see with dark matter.

Not having a dog in this fight, I'm just wondering how "non-relativistic neutrinos" travel at relativistic speeds.

Whoops, missed the "non" bit in his question. Still, because they *were* once moving at relativistic speeds, their energy has dropped off so much that they are now pretty insignificant (although they still do have an effect, albeit a minor one) energy wise. They also don't work to explain the evolution of the large-scale structure in the universe that we can see, which pretty much requires cold matter.

According to the STVG page, the current version of the modified-gravity theory seems to be holding up well. But I don't know much about it beyond that, so if you have any links to things it doesn't address, I'd appreciate it.

This.

I'd like to know what disproves, or at least casts doubt, on MoND (really SVTG/TeVeS now). CMB anisotropies are often cited as something TeVeS can't explain. What else is there?

We don't 'know' there is dark matter despite these observations. Another explanation instead of dark matter is modified gravity of some sort over the large scale.

Modified gravity has mostly been disproven, but not with the "5 sigma" strength required yet. They have measured gravity over long distance and have shown it to be within 99.9% of our expected value, meaning modified gravity does not fit.

There are also other phenomena that must be explained, like gravitational lensing where no observable mass is. Something MUST be there, yet we see nothing. Not just dark, but actually transparent. All normal matter in the universe interacts with light, but whatever this is, it does not. We're talking about galaxies worth of matter, not some slight difference.

That's because the blog you linked assumes that Mond replaces the extra mass in the universe. Ethan begins with the premise that it has to be one or the other.

Both could be true.

Yes, the point of the blog is that DM-free theories do not match reality at all, and therefore alternate gravity theories cannot, according to empirical data, replace Dark Matter.

Which is the context in which alternate gravity theories were brought up in this very thread -- as they usually are any time Dark Matter comes up. I've never even heard anyone bring up MOND outside of a discussion of DM and how that might not be the right explanation.

You're obviously against the DM hypothesis yourself, so if you are going to talk about MOND or TeVeS in the context of "Maybe GR is still wrong, but not in a way that obviates the need for Dark Matter" then you should make that very explicit please and thank you.

"Nearly every extension to the [Standard Model] introduces new CP violating phases." So, those extensions dictate that the electron should have an electric dipole moment. The smaller the dipole moment, the heavier the particle involved in its creation.

Is that really as broad as it sounds? Because as far as I know, things like neutrinos with mass (pretty well verified by experiment) are only possible as modifications of and extensions to the Standard Model.

Also, anyone else see the EDM in the project name and think of Wile E. Coyote hunched over a turntable and mixers?

That's because the blog you linked assumes that Mond replaces the extra mass in the universe. Ethan begins with the premise that it has to be one or the other.

Don't needlessly multiply entities. From the evidence, a mix of MOND and dark matter won't improve models, so why consider it? The only reason MOND is postulated in the first place is to avoid the need for dark matter, and if you accept the existence of dark matter, you no longer have any reason to consider MOND.

As for neutrinos, no, they can't be any more than a small fraction of dark matter. However, they certainly qualify as one kind, and are a counterexample to the argument that dark matter is somehow inherently absurd just because it involves weakly-interacting particles.

Not being a physicist, but having a more than passing interest in the subject, I often wonder one little thing: Why is the whole "dark matter" thing a question of looking for exotic particles?

I get that given the rotational speeds of galaxies, there should be more mass than can be detected, but exactly how is the mass being seen in the first place? At massive distances, we're talking about only that which can be measured by instruments. That requires mass to have some kind of detectable emission - visible, infrared, ultraviolet, x-ray, gamma ray, etc. At intergalactic distances, how much of what we get comes from essentially non-energetic mass?

You know, rocks.

I get that dust is out there and easily detectable because it's spread out over such a large area. But if you put that dust together, you end up with rocks and a lot less dust. Look at our neighborhood. Lots and lots of rocks. Very little dust. The basic concept is that most matter has coalesced from dust into more solid objects, but those solid objects aren't as easily detectable because they have low surface areas with regard to the radiation they receive and reflect.

Another aspect that I think isn't really explained with regard to "seen mass" versus the mass needed to explain the speed of rotation observed is simply inert black holes. Because, let's face it, you're not going to detect one of those (except gravitationally) with instruments unless it's feeding. It seems to me I read an article not too long ago that postulates a large number of basically inert black holes wandering around galaxies, all made up from a bunch of rocks.

At 3.8 solar masses (the currently smallest stable black hole observed) and up, if there are enough of these stable non-interacting Black Holes (SNIB's) out there that just aren't being detected by current science, you're looking at significant amounts of mass that is essentially normal.

Yes, this is likely a hideously simplistic point of view, but let's face it: We don't know what's out there for sure. We're operating on observation and theory - the latter of which keeps changing as we obtain more and more data from the former. And the former seems to be indicating that there's more mundane matter out there (Assuming black holes can be called mundane) than we thought.

While I don't think any reasonable avenue of research should be abandoned, I often think that some more reasonable avenues of research should be more thoroughly explored before wandering off on exotic matter side tracks. It just seems to me that we have glossed over or ignored the more mundane things that are out there, in spite of a small, but growing, body of evidence to suggest our original formulas of how much normal matter makes up the composition of a galaxy may be off. I'd love to hear why we have apparently ruled that entirely out as the source of our observations (or at least a link to someplace that explains WHY mundane matter CAN'T be the missing "dark matter") in the pursuit of something more exotic.

Like I said, I'm only an enthusiast in physics. But this part of the whole dark matter thing has always bothered me and to date, all I hear is "there isn't enough matter to explain..." without explaining how that conclusion was achieved.

Not being a physicist, but having a more than passing interest in the subject, I often wonder one little thing: Why is the whole "dark matter" thing a question of looking for exotic particles?

I get that given the rotational speeds of galaxies, there should be more mass than can be detected, but exactly how is the mass being seen in the first place? At massive distances, we're talking about only that which can be measured by instruments. That requires mass to have some kind of detectable emission - visible, infrared, ultraviolet, x-ray, gamma ray, etc. At intergalactic distances, how much of what we get comes from essentially non-energetic mass?

You know, rocks.

I get that dust is out there and easily detectable because it's spread out over such a large area. But if you put that dust together, you end up with rocks and a lot less dust. Look at our neighborhood. Lots and lots of rocks. Very little dust. The basic concept is that most matter has coalesced from dust into more solid objects, but those solid objects aren't as easily detectable because they have low surface areas with regard to the radiation they receive and reflect....

That much dust would make it impossible to get light through the universe very far. Even enough hydrogen atoms floating around freely to make up the discrepancy would have absorbed the cosmic background microwave radiation long ago.

The missing mass of galaxy rotational speeds isn't just a missing mass problem. The mass distribution is all wrong. The dark matter is not clustering to the gravitational center like normal matter. This suggests that while it's affected by gravity it's not "clumping" so it doesn't interact with itself very much never mind normal matter.

Edit: excellent book on the subject for technical types but non-physicists is The 4% Universe. That will explain it far better than I can.

Not being a physicist, but having a more than passing interest in the subject, I often wonder one little thing: Why is the whole "dark matter" thing a question of looking for exotic particles?

You know, rocks.

Agree with Wickwick, and also look at the MACHO project. Essentially small things like rocks obscure too much, and big things like planets or small black holes would gravitationally lens background stars. They went looking for the lensing, and while they found lensing it was consistent with expectations for star to star lensing and not anywhere enough to explain dark matter.

So we're looking for particles because rocks and small black holes have already been ruled out.